In Planet of the Apes, ANSA astronaut George Taylor and his crew aboard the Icarus crash-land back on the planet Earth in the year 3978. This date is found in two different references. The year 3978 is visibly shown on the ship's date-meter moments after crashing into the lake, and it is also found as part of the interactive menu screen on the Planet of the Apes DVD from the Evolution collection.

In Beneath the Planet of the Apes however, another astronaut named John Brent lands on Earth some months after the events chronicled in the first film. When speaking with his dying comrade, he indicates that the year is 3955 – more than twenty years prior to the events from Planet of the Apes.

This year is again referenced in the second sequel, Escape from the Planet of the Apes. While under the influence of Grape Juice Plus, Dr. Zira confesses that the date meter on the ship she was one read, "...thirty-nine fifty... something." It is important to note, that Zira had returned to Earth's past aboard the Icarus, and not Brent's ship, even though the Icarus' terminal never indicated a year of 3955 on-screen.

Reconciling the two conflicting dates is virtually impossible (though in the 2017 essay anthology Bright Eyes, Ape City: Examining the Planet of the Apes Mythos, Joe Dilworth suggests that Brent’s date-meter, though faulty, could have been salvaged by Milo to replace that from Taylor’s water-logged ship[1]). For the sake of consistency, The Sacred Scrolls is treating the year 3978 as the canonical year of events for both Planet of the Apes and Beneath the Planet of the Apes. All other dates that correspond to either film, including birth-dates, date of death, etc. will be relative to the year 3978.